<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./js/vue.js"></script>
</head>
<body>
    <div id="app">
        <div>{{flag}}</div>
        <div>{{un}}</div>
        <div>{{n}}</div>
        <div v-if="flag">你好</div>
        <div v-show="flag">他好</div>
    </div>
    
</body>
<script>
      new  Vue({
        el:"#app",
        data:{
            flag:false,
            un:undefined,
            n:null   
        },
        methods:{
         
          
        }

      })

</script>
</html>